This invention relates to the field of injection molding into useful articles of polymeric raw materials and, more specifically, includes methods and apparatus for feeding the polymeric raw materials from a hopper into the interior of an injection molding machine.
Injection molding machines generally include a funnel-shaped hopper for holding polymeric raw material to be used in the injection molding process. The polymeric raw material typically is in the form of small pellets, for example, on the order of 1/8" in diameter and up to 3/8" in length. Typical polymeric raw materials include nylons, polyacrylates, polycarbonates, polyvinylchloride resins, ABS resins, polyolefins or other polymeric material. The hopper is filled by a loader which includes vacuum apparatus for sucking the pellets from a sack, drum or other receptacle in which they have been received for processing and depositing the pellets in the hopper. The hopper is positioned over the trunnion inlet to the injection molding machine. The pellets flow due to gravity out of the bottom of the hopper and into the interior of the injection molding apparatus. Additionally, it is common practice to insert a magnet box between the hopper and the trunnion to collect metal foreign material such as nuts and bolts, to keep them from entering the injection molding machine. It is also common to insert a color mixer between the hopper and the trunnion, optionally in combination with a magnet box, for providing color powders or other materials to be mixed with the polymeric material pellets. The hoppers in commercial use are designed to hold up to several thousand pounds of raw materials.
Generally, after an injection molding run or job is completed, the hopper is emptied of unused material, cleaned out if necessary, and reloaded with new material for a subsequent job. Because of its weight and bulk, removing and repositioning the hopper is difficult and time-consuming, often requiring the use of a lift truck, crane or other heavy machinery. While the hopper is moved aside for emptying or cleaning, the injection molding machine lies idle, thereby diminishing the productivity of the overall operation. If a second hopper is available, the machine is idled while the second hopper is moved into place, bolted on and loaded.
Often, it is also necessary to dry the raw material pellets before they are used in the injection molding process. To do so, the pellets are first loaded into a hopper, then a dryer is attached to the hopper and operated to dry the pellets. This procedure can take several hours. After the material is dry, the hopper can be mounted on to the trunnion to begin the injection molding process. Thus, drying also causes substantial down-time of the injection molding machine. Where a second hopper is incorporated for drying, it is nonetheless necessary to reposition the hoppers, as described above, as part of the injection molding process.
Accordingly, a need exists to improve the productivity and efficiency of injection molding operations by reducing the down-time occasioned by handling, clearing and cleaning input hoppers.